This invention relates to methods of screening for compounds capable of inducing apoptosis in certain tumor cells. The invention also relates to compounds identified by such methods. In addition, the invention relates to methods for the in vitro diagnosis of Xeroderma pigmentosum and compounds useful in these methods.
Certain tumors, benign, premalignant, and malignant, are known to have genetic components etiologically. The gene for the nuclear phosphoprotein, p53, is the most commonly mutated gene identified in human cancers. Missense mutations occur in tumors of the colon, lung, breast, ovary, bladder, and several other organs. When mutant forms of the p53 gene are introduced into primary fibroblasts, these cells are immortalized. The wild type p53 gene can suppress the growth of transformed human cells, but oncogenic forms lose this suppressor function. Thus, the p53 gene has been termed a "tumor suppressor" gene.
If the p53 gene of a tumor cell is of the wild type, its p53 gene product may nevertheless be interfered with functionally. For example, a transforming viral infection of the cell can interfere with the p53 protein product. For instance, certain strains of human papillomavirus (HPV) are transforming and are known to interfere with the p53 protein function because the virus produces a protein, E6, which promotes degradation of the p53 protein.
There is also pharmaceutical interest in p53 because p53 protein is capable of inducing certain tumor cells to undergo apoptosis. In apoptosis, or "programmed cell death", a series of lethal events for the cell appear to be generated directly as a result of transcription of cellular DNA. Thus, apoptosis is a physiologic means for cell death. For example, lymphocytes exposed to glucocorticoids die by apoptosis. Involution of hormone sensitive tissue such as breast and prostate that occurs when the trophic hormone is removed occurs via apoptosis.
In particular, recent studies have indicated that the introduction of wild type (non-mutated) p53 into transformed cell lines that carry a mutant form of p53 induces the cells to undergo apoptosis with disintegration of nuclear DNA. It is believed that p53 may suppress tumor development by inducing apoptosis, thus modulating cell growth.
In addition to p53, there are numerous other genes involved with cell growth. One group of such genes is designated XP because their derangement can result in the disease Xeroderma pigmentosum. Xeroderma pigmentosum is a rare disorder characterized by disfigurement, deranged pigmentation of the skin, scarring and heightened incidence of skin cancers, especially on exposure to sunlight. The disease is inherited as an autosomal recessive trait. Eight genetic forms of the disease are known. Phenotypically these forms vary in their symptoms, signs and severity. Two of the more grave forms are associated with mental deficiencies. These two forms are characterized by mutations in the XPB and XPD genes.
Selection of drugs for potential therapeutic use against tumors is an area of medical research which remains fraught with complications and which often present an array of suboptimal treatment choices. There are currently a multitude of potential compounds available to evaluate. Screening procedures are valuable to limit the bewildering array of drug choices for further testing. Improvements in screening methods or reagents are highly desirable. In addition, there is a need for better diagnosis of XP subtypes. These and other needs are addressed by the present invention.